Harmonic Distortion Levels Measured at The Enmax Substations

Transcription

1 Harmonic Distortion Levels Measured at The Enmax Substations This report documents the findings on the harmonic voltage and current levels at ENMAX Power Corporation (EPC) substations. ENMAX is concerned about the harmonic impact of future HVDC converters to be implemented close to its substations. The U of A team initiated this project to help addressing the concern. The approach is to measure, analyze and compare the harmonic currents and voltages at substations close to the future converter stations before and after the HVDC energization. Harmonic voltage and current field measurements were carried out during a one-week period in August 2011 at several ENMAX substations. This is the first time to collect the data. Similar measurements are planned for next year and thereafter. The collected data have been analyzed and presented through typical PQ indices and under different perspectives in order to facilitate comparison with future field measurements. The results include the daily profiles as well as the statistical distributions of the harmonic voltage and current at both phase and sequence domains.

2 Wire to Earth Voltage Comparative Analysis for Underbuilt Circuits Power line faults create the ground potential rise (GPR) on both the neutral and shield conductors when the transmission lines and distribution lines are built on the same structures. This study analyzes and compares the safety impacts of T- line faults and distribution line faults in the joint structures. First, the GPR mechanisms are illustrated and approximate formulas are established to describe the GPR characteristics. This project presents results on the GPR at the multigrounded neutral points of a distribution line and at the multi-grounded shield points of a transmission line where the distribution line is installed below a transmission line in the same tower structure. The GPR results of such a configuration are compared to those associated with common single circuit configurations. The results are obtained through extensive analytical studies and computer simulations. It was found that the under-built multi-grounded (MGN) distribution line does not increase the shield potential rise (SPR) of the corresponding transmission line when a distribution line is added. In comparison to the neutral potential rise (NPR) produced by a distribution line fault, the MGN neutral points will generally experience higher NPR when a fault occurs in the overbuilt transmission line.

3 Truck Grounding Issues Investigation A utility truck working under power lines may experience several safety risks, with the touch voltages produced by accidental contacts with energized lines being the primary concern. Utility companies have used a few grounding schemes to reduce these risks. The representative schemes are (1) ungrounding the truck, (2) bonding the truck to a temporary rod1, (3) bonding the truck to a system rod (i.e., the grounding point of the system neutral), and (4) bonding the truck to the system neutral. Each scheme involves its own work procedure, but no scheme can guarantee complete safety. As a result, utility companies in North America do not agree about which grounding scheme can lead to the best practice. In order to help the Alberta utility companies to make an informed decision on this subject, the Alberta Power Industry Consortium established a project to investigate the truck-grounding issues. The objective is to clarify and quantify the safety risks associated with the different truck-grounding schemes. It is hoped that the project findings will provide a technical background and support to the committees involved in establishing safe working practice. To fulfill the above objective, the research has been approached from the following three aspects: (a) options to increase worker safety, (b) quantitative assessment of the other concerns associated with different grounding schemes, and (c) comparing different grounding schemes. Through a complete study, this project has identified four safety options for utility companies to consider: 1) grounding (grounding to the system neutral (or rod), or no grounding at all), 2) barricading, 3) using an isolation mat, and 4) wearing insulating boots/gloves. By combining the above four safety options, all the possible safety packages for consideration by utility companies have been provided. 1 Temporary rod in this research refers to any grounding rod that is not connected to a multi-grounded neutral conductor. In other words, if there is no neutral in a feeder, all grounding rods are referred as temporary rod although they may exist permanently in the system. The electric performance of such rods is similar to the temporally created isolated rods.

4 Measuring the Supply System Impedance Parameters The equivalent circuit parameters of a power supply system such as the shortcircuit impedance are important data for both power supply authorities and industrial customers. The parameters have several applications. They are used to calculate the short circuit currents and to verify models of power system networks. The data are also needed for VAR compensator and harmonic filter designs to avoid creating resonance conditions. This project proposes a new method for online tracking of power system impedance parameters, which include the positive and zero sequence impedances and the harmonic impedances. The algorithm can be implemented into the power monitors widely available in load serving substations. The proposed algorithm is independent of load models and does not require synchronized data. So it overcomes the shortcomings of existing methods. Furthermore, practical implementation issues are addressed in the project and the proposed method has been verified using computer simulations, experimental studies, and several field measurements.

5 Measuring the Load Model Parameters The loads in power systems play an important role in power system planning, control and stability analysis. Having reliable and accurate models of the loads is essential for the purpose of designing automatic control systems and optimization of their configuration. Obtaining detailed and accurate models of power system loads can be a more complicated task than modeling other power system components, such as a synchronous machine. The reason is the large number of different loads, such as lighting, motor load heating, etc. and the complexity and random nature of their composition. The accurate load modeling has been a challenging problem for power system engineers for decades, especially in the deregulated market environment. Regarding the importance of the issue two basic approaches have been proposed in literature to model the composite loads in power system studies, namely, component-based and measurement-based. The component-based approaches build up the load model from information on the behaviors of all the individual components and load components of a particular load bus. The componentbased approach has the disadvantage of requiring performance of an extensive survey to collect load composition information, but, after deregulation, transmission system planners may not be able to access such information. The measurement-based approach involves installing measurement and data acquisition devices at various load buses to determine model structures and model parameters. They have the obvious advantage of obtaining data directly from the actual system. As well, these techniques can directly measure actual load behaviors and the parameters for the measurement-based load modeling approach can be easily updated when the load characteristics change. This project proposes a new method for online measurement and monitoring of power system load model parameters. The advantage of the proposed algorithm is the simple implementation and its ability to be applied for real-time monitoring of load parameters. Furthermore, practical implementation issues are addressed in the project and the proposed method has been verified using several field measurements. Details are omitted here due to patent filing.

6 Techniques and Software for Harmonic Source Detection in Power Systems There are many harmonic loads in a given distribution or sub-transmission system. These loads typically have comparable sizes and are scattered all over the system. Identifying loads that actually causes a reported harmonic problem has become an increasingly important task for utility power quality management. Unfortunately, there are no viable techniques that can pinpoint which customers cause harmonic distortions problem at a specific location of a system. This report presents a data-based method and associated technique for determining the individual harmonic impact of multiple harmonic-producing loads scattered in a power system. The report defines the problem and proposes a harmonic impact index to theorize the problem. It then presents a statistical inference based method to estimate the index. The data required for this analysis are the harmonic voltage and current magnitudes continuously collected by existing power quality monitors. To facilitate technology transfer to the consortium members, this method is implemented in a software package. A tutorial of the software and two application examples are provided in the report. The characteristics of the proposed method are also investigated through sensitivity and case studies. Finally, some notes about single-point applications of the proposed method are discussed.

7 Survey of High Impedance Fault Detection Techniques High Impedance Faults (HIF) usually occur at primary network level in electrical distribution systems. They can be described as those faults which do not draw sufficient current to be recognized and cleared by the over-current devices in common use in the utility industry. Research on high impedance fault detection has been conducted for decades. However, a complete solution has not yet been found. Not only is the current too small, but also because distinguishing high impedance faults from normal operations are very complicated as various normal operations unfortunately create the similar transient as HIF. The development of high impedance faults detection techniques are reviewed in this paper while individual techniques are analyzed. Those techniques based on voltage and current measurement can be classified into time domain and frequency domain algorithms. However, it is realized that so far no single detection algorithm could reliably identify a majority of HIF faults. Moreover, no single detection technique could both protect the public from the dangers of a downed conductor and minimize unnecessary power outages from false trips. A Composite system with multiple fault detection algorithms is a solution to overcome the limitations and disadvantages of single algorithms. The features of a composite system are introduced and the decision logic is analyzed. Moreover, alternative solution including mechanical technique and remote techniques are presented. Finally, possible improvements are proposed at the end of this report.

8 Substation GPR Transfer to Feeder Neutral Points The objective of this project is to investigate the neutral potential rise (NPR) of the MGN feeders due to short-circuit within substation boundaries. Analytical studies are performed to illustrate how the neutral potential rise (NPR) arises due to substation GPR. The NPR transfer to the downstream loads is estimated by establishing the simplified equations. The effects of system arrangements as well as the impact of the multi grounded neutral parameters are shown through case study results. The main findings of the report can be summarized as follows: The mechanisms involved in the GPR production are the same for the T- side faults and for the D-side faults and it is independent of the fault location in the substation. The NPR at the grounding points of MGN increases with the increase in neutral grounding resistances or grounding intervals. The neutral length has significant impact of the NPR profile, the shorter the neutral length; the higher will be the NPR at its end. However, the maximum NPR will be affected only slightly The grounding resistance of the first load downstream of the substation will affect the transferred NPR to this point, especially when the neutral is 2 km or less. In summary, general models for estimating the substation GPR and the maximum NPR have been established. This study is also applicable for the system where a multi-grounded conductor (shield, neutral, etc) is extended from the substation. Furthermore this study can be generalized for any number of feeders (single or multiple parallel feeders).

9 Measurement and Analysis of Harmonics in Residential Distribution Feeders Distribution system harmonic study was traditionally focused on the analysis of networks with dominant harmonic sources at known locations. They are usually associated with large individual industrial loads. With the proliferation of the harmonic producing loads, such as computers and variable speed drives, the harmonic sources become more and more randomly distributed into all over the network. Nowadays, every residential house could be a small harmonic source. And the collective effect of those distributed harmonic source has been of a great interest and a significant power quality concern. It can be summarized into two features: 1) those harmonic sources are usually random and small. 2) they are dispersed into everywhere through the whole distribution system. According to these characteristics, traditional harmonic analysis and mitigation methods may not be applicable anymore. It is urgent to understand the mechanism of harmonics build up in residential feeders whose loads are essentially distributed harmonic sources, and furthermore propose a system-wide harmonic analysis method and new strategy to design a novel filter to handle this kind of problem. This has become a new challenge to harmonic area. This project is one of the projects sponsored by the Alberta Power Industry Consortium. It first comes along with the telephone interference problems found in some residential neighborhoods in Edmonton, Canada. Month-long measurement has been carried out. These valuable measurements data helps to understand the harmonic behavior in the new circumstance, eventually, the corresponding theory and strategy to interpret and resolve this new problem will be developed.

10 Determining Acceptable AIES System Restoration Island Synchronizing Parameters This project investigates the main technical issues associated with the resynchronization of islanded Alberta Integrated Electric System (AIES). It determines if the current synchronization relay settings are adequate and recommends changes if required. Through a series of analytical and simulation studies, the impact of each synchronization parameter (voltage magnitude, phase angle and frequency differences at the synchronization points) on generators and overall system performance has been identified. The study further established analytical methodologies for interpreting the simulation results by revealing the nature and mechanism of the synchronization disturbances. Synchronization protection settings for AIES are recommended. One of the findings is that the generator-system synchronization produces the highest transients on the generators in comparison with the island-island synchronization cases when same synchronization criteria are used. The implication is that if one adopts the relay settings of generator-system synchronization to island-island synchronization, the impact of the synchronization transients on the generators will be less than that produced by the generator-system synchronizations.

11 Guide for Utility Motor Starting Planning The power quality impact of motor starting is a concern to utility companies. This concern is especially important in Alberta due to the presences of a large number of industrial facilities and the relatively long distribution lines. Although there are various ways to reduce the impact of motor starting, almost all of the solutions need to be planned and designed before the motor and its facility are connected to the system. Furthermore, new power quality standards such as the IEC flicker meter are gaining acceptance and it has become necessary to consider these standards when conducting the motor starting planning studies. The objective of this report is to provide technical information to support the motor starting planning study from the utility s perspective. The report attempts to address all key issues involved in the study and to provide practical ways for efficient motor starting impact assessment. The topics covered by this report include 1) power quality issues associated with motor starting, 2) customer and utility side solutions to the motor starting problems, 3) methods for motor starting study and 4) practical tools for quick screening of motor starting problems. These practical tools, called motor starting guideline charts, are developed according to the latest IEEE power quality standards. It helps a planning engineer quickly estimate if a motor installation can cause voltage sag or voltage flicker problems. He or she can then decide if detailed motor starting study is required.